Carrier to noise thresholds


Carrier to noise and particularly carrier to noise threshholds are of increasing interest to us. The threshhold defines the point at which the DVB-T [COFDM] reception system will fail [below the error free point]. It is that digital cliff edge. The chart shows various modulation scheme and I have highlighted our COFDM variants in RED and the Foxtel/Austar satellite transmission in GREEN.

C/N Threshold minimum performance for QEF reception.

Modulation
FEC rate
Gaussian
Rican
Rayleigh
QPSK
½
5.6
6.1

7.9
Transponder T10a only
QPSK
2/3
7.4
8.2
10.9
QPSK
¾
8.4
9.3
13.2
QPSK
5/6
9.4
10.5
15.6
QPSK
7/8
10.2
11.2
18.8
16QAM
½
11.3
12.1
13.7
16QAM
2/3
13.6
14.1
16.7
16QAM
¾
15.0
15.5
19.2
16QAM
5/6
16.0
16.9
21.8
16QAM
7/8
16.4
17.5
25.3
64QAM
½
16.9
17.2
18.5
64QAM
2/3
19.0
19.6
21.8
64QAM
¾
20.5
21.1
24.2
64QAM
5/6
21.8
22.5
27.8
64QAM
7/8
22.6
23.5
30.4"

 

 

 

 

 

 

 

 

 

 

For terrestrial [COFDM] transmissions:

Gaussian - ideal single direct path reception apart from the addition of white Gaussian noise. Typical of country reception using a outdoor antenna for distant "line of sight" reception with no significant multipath.

Rican – a channel with a prominent direct path between transmitter and receiver, but with a number of echoes also present. Typical of suburban reception where a outside antenna is used.

Raleigh - a channel with no direct path between transmitter and receiver, but with a number of echoes present. Typical of city indoor reception using "rabbit ears" type antenna."